The overall aim of this proposal is to understand mechanisms underlying color discrimination, including how visual pigment spectral sensitivity is regulated and how information about color in the environment is integrated into the behavior of a living organism. The studies will focus primarily on Drosophila, which use visual pigments with unique spectral properties that can be characterized using well-developed spectral and physiological techniques. The ability to manipulate the organism genetically allows many interesting questions concerning eye and visual pigment function to be addressed in vivo. The relationships of visual pigment structure to spectral sensitivity and physiological properties will be examined. In addition, the visual pigments of other invertebrate organisms will be examined. These efforts to heterologously express such pigments in Drosophila and to characterize their spectral sensitivity using physiological methods are the only examples of cloned invertebrate opsins from an organism other than Drosophila that have been successfully expressed and characterized in any system. The final area of research concerns a set of behavioral studies designed to better characterize the functional role of specific classes of photoreceptor cells and the ability of flies to discriminate colors. The wealth of behavioral information available from Drosophila and other invertebrate systems will be used in combination with modern molecular genetic techniques to begin a functional dissection of color discrimination. These complementary approaches should ultimately provide a more comprehensive understanding of how color information about the environment is encoded, processed and used by the organism.